Engineering Drawing Notes

1
ME170 Computer Aided Design
Engineering Drawing Notes Part B Coordinate
Dimensioning Tolerancing
Instructor Mike Philpott Associate Professor
of Mechanical Industrial Engineering
2
Contents

• 2D Drawing Principles
• Coordinate Dimensioning Tolerancing
• ANSI/ISO Tolerance Designation
• ANSI/ISO Classification of Limits and Fits
• Surface Properties
• Economics of Tolerances/Surface properties
• Geometric Dimensioning and Tolerancing (GDT)

Part A
Part B
Part C
Attention to Detail The engineering drawing is
the specification for the component or assembly
and is an important contractual document with
many legal implications, every line and every
comment is important.
3
Coordinate Dimensioning and Tolerancing
The collective process of modeling, defining and
describing geometric sizes and feature
relationships, and providing all of the required
technical information necessary to produce and
inspect the part is called dimensioning and
tolerancing. The current National Standard for
dimensioning and tolerancing in the United States
is ASME Y14.5M - 1994.
DRAWN IN ACCORDANCE WITH ASME Y14.5M -
1994 REMOVE ALL BURRS AND SHARP EDGES ALL
FILLETS AND ROUNDS R .06 UNLESS OTHERWISE
SPECIFIED
4
Drawing Notes
Notes should be concise and specific. They
should use appropriate technical language, and be
complete and accurate in every detail. They
should be authored in such a way as to have only
one possible interpretation.
General Notes
DRAWN IN ACCORDANCE WITH ASME Y14.5M -
1994 REMOVE ALL BURRS AND SHARP EDGES ALL
FILLETS AND ROUNDS R .06 UNLESS OTHERWISE
SPECIFIED
Local Notes
4X 8.20 M10 X 1.25 82º CSK 10 1.5 X
45º CHAM
5
Line Types

• Object Lines
• Hidden Lines
• Center Lines
• Phantom Lines
• Dimension Lines
• Extension Lines
• Leader Lines
• Cutting Plane Line
• Sections - Hatching
• Break Lines

thick
thin
thin
thin
thin
thick
thin
thick
6
Arrowheads

• Arrowheads are used as terminators on dimension
  lines. The points of the arrowheads on leader
  lines and dimension lines must make contact with
  the feature object line or extension lines which
  represent the feature being dimensioned. The
  standard size ratio for all arrowheads on
  mechanical drawings is 31 (length to width).

Of the four different arrowhead types that are
authorized by the national standard, ASME Y14.2M
1994, a filled arrowhead is the highest
preference.
4th
1st
2nd
3rd
7
Dimension Lines and Extension Lines
Extension lines overlap dimension lines (beyond
the point of the arrowheads) by a distance of
roughly 2-3mm
1.75
There should be a visible gap (1.5 mm) between
the object lines and the beginning of each
extension line.
1.06

• Dimensions should be placed outside the actual
  part outline. Dimensions should not be placed
  within the part boundaries unless greater
  clarity would result.

8
Placement of Linear DimensionsOrder of Preference
Arrows in / dimension in
2.562
Arrows out / dimension in
1.250
Arrows in / dimension out
.750
Arrows out / dimension out
.500
When there is not enough room between the
extension lines to accommodate either the
dimension value or the dimension lines they can
be placed outside the extension lines as shown in
the fourth example (use Flip Arrows in ProE).
9
Reference Dimensions
Reference Dimension Symbol (X.XXX)
EXAMPLE

• Reference dimensions are used on drawings to
  provide support information only.
• They are values that have been derived from other
  dimensions and therefore should not be used for
  calculation, production or inspection of parts.
• The use of reference dimensions on drawings
  should be minimized.

2.250
(.750)
1.000
.500
.500
1.250
.500
(.750)
10
Location of Dimensions
Shorter (intermediate) dimensions are placed
closest to the outline of the part, followed by
dimensions of greater length. Dimensions nearest
the object outline should be at least .375 inches
(10 mm) away from the object, and succeeding
parallel dimension lines should be at least .250
inches (6 mm) apart.
.250 (6mm) Minimum Spacing
4.375
1.438
1.250
.375 (10mm) Minimum Spacing
1.000
1.875
1.062
.688
2.312

• Dimensions should be placed outside the actual
  part outline

11
Basic Dimensioning Good Practice
4.375
1.438
1.250
1.000
1.875
1.062
.688
2.312
Extension lines should not cross dimension lines
if avoidable
In-line dimensions can share arrowheads with
contiguous dimensions
1.250
1.438
1.000
1.875
1.062
.688
2.312
BETTER
4.375
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Diameter Dimensions Holes and cutouts
1.375
.625 THRU
.250
.62
.250 x .62 DP
1.375
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Diameter Dimensions Shafts and Holes

• Whenever it is practical to do so, external
  diameters are dimensioned in rectangular (or
  longitudinal) views. Cylindrical holes, slotted
  holes, and cutouts that are irregular in shape
  would normally be dimensioned in views where
  their true geometric shape is shown.

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Placement with Polar CoordinatesTo dimension
features on a round or axisymmetric component
18º
18º
3X .562
3.50
6X .188
.875
18º
18º
18º
18º
15
Radial Dimensions To indicate the size of
fillets, rounds, and radii
R.312
R14.25
R.750
R.312
R.562
16

• Angular Dimensions
• To indicate the size of angular details appearing
  as either angular or linear dimensions.

92º
2 x 45º
63º
Alternate
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Times and By Symbol X

• The X symbol can also be used to indicate the
  word by. For instance, when a slot that has a
  given width by a specified length, or a chamfer
  that has equal sides (.12 X .12).
• When used to imply the word by, a space must
  precede and follow the X symbol.
• If the same feature is repeated on the drawing
  (such as 8 holes of the same diameter and in a
  specified pattern), the number of times the
  instruction applies is called out using the
  symbol X.

.12 X 45º CHAMFER
.375 .562 X 82º
CSK
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Drilled Holes

• Normally specified by diameter and depth (or THRU
  note used).

45
12.5
?
14 THRU
25
90
12
50
12.5
?
2x 12 THRU
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Specify reaming if accuracy/finish is important.
25
12
90
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ASME/ANSI Hole Depth Symbol

• Features such as blind holes and counterbores,
  must have a depth called out to fully describe
  their geometry.

Depth or Deep Symbol
EXAMPLE
.625
.375 .625
OR
.375
This symbol is currently not used in the ISO
standard. It has been proposed.
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ASME/ANSI Countersink Symbol
Countersink Symbol

• The symbol denotes a requirement for countersunk
  holes used to recess flathead screws. The
  height of the symbol is equal to the letter
  height on the drawing, and the included angle is
  drawn at 90º. Note that this symbol is not used
  in the ISO (international) standard.

EXAMPLE
This symbol is currently not used in the ISO
standard. It has been proposed.
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ASME/ANSI Counterbore Symbol

• This symbol denotes counterbored holes used to
  recess machine screw heads.

Counterbore Symbol
EXAMPLE
.312
.562
.375
OR
This symbol is currently not used in the ISO
standard. It has been proposed.
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Counterbores and Countersinks ISO Standard
2 x
50
?
8.8 THRU
12.5
?
14 C BORE x 8.2 DP
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Socket Cap Head or Machine screws
25
12
90
2 x
50
?
8.8 THRU
12.5
32
?
15 CSK
Flat Head
25
90
12
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Screw Threads
M 16 x 2
ISO specify metric only
M 16 x 2 - 4h - 5H
Class of fit of mating thread (optional)
ISO metric designation
Nominal Diameter (mm)
Thread Pitch(mm)
Class of fit of this thread (optional)
3/4 - 10 - UNC
American Unified Threads

3/4 - 10 - UNC - 2A
Thread Type (optional) AExternal BInternal
Nominal Diameter (inches)
Threads per inch
Class of fit (optional)
Thread Series UNC Unified Coarse UNF Unified
Fine
Note Use standard screw sizes only
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Threads and Screw Fastening
Example Assembly
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Threads and Screw Fastening (cont.)
Base Detail
26

Threads and Screw Fastening (cont.)
3 Holes
??
12.7 THRU
EQ SP on
?
120 PD
Lid Detail
'A'
Section 'A'-'A'
'A'
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Tolerancesimportant to interchangeability and
provision for replacement parts

• It is impossible to make parts to an exact size.
  The tolerance, or accuracy required, will depend
  on the function of the part and the particular
  feature being dimensioned. Therefore, the range
  of permissible size, or tolerance, must be
  specified for all dimensions on a drawing, by the
  designer/draftsperson.
• Nominal Size is the size used for general
  identification, not the exact size.
• Actual Size is the measured dimension. A shaft
  of nominal diameter 10 mm may be measured to be
  an actual size of 9.975 mm.
• General Tolerances
• In ISO metric, general tolerances are specified
  in a note, usually in the title block, typically
  of the form "General tolerances .25 unless
  otherwise stated".
• In English Units , the decimal place indicates
  the general tolerance given in the title block
  notes, typically
• Fractions 1/16, .X .03, .XX .01, .XXX
  .005, .XXXX 0.0005,
• Note Fractions and this type of general
  tolerancing is not permissible in ISO metric
  standards.

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Specific Tolerances
Specific Tolerances indicate a special situation
that cannot be covered by the general tolerance.
Specific tolerances are placed on the drawing
with the dimension and have traditionally been
expressed in a number of ways
0.05 - 0.03
40.05 39.97
0.04
-
40.01
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Bilateral Tolerance
Unilateral Tolerance
Limit Dimensions

• Limits are the maximum and minimum sizes
  permitted by the the tolerance. All of the above
  methods show that the dimension has
• a Lower Limit 39.97 mm
• an Upper Limit 40.05 mm
• a Tolerance 0.08 mm
• Manufacturing must ensure that the dimensions are
  kept within the limits specified. Design must not
  over specify as tolerances have an exponential
  affect on cost.

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Limits and Fits
1. Clearance Fits The largest permitted shaft
diameter is smaller than the diameter of the
smallest hole
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• 2. Interference Fits
• The minimum permitted diameter of the shaft is
  larger than the maximum diameter of the hole
• 3. Transition Fits
• The diameter of the largest allowable hole is
  greater than that of the smallest shaft, but the
  smallest hole is smaller than the largest shaft

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Standard Limits and Fits -- ANSI
Extract from Table of Clearance Fits
RC 1 Close sliding fits are intended for the
accurate location of parts which must assemble
without perceptible play. RC 2 Sliding fits are
intended for accurate location, but with greater
maximum clearance than class RC 1. Parts made to
this fit move and turn easily but are
not intended to run freely, and in the larger
sizes may seize with small temperature
changes. RC 3 Precision running fits are about
the closest fits which can be expected to run
freely, and are intended for precision
work at slow speeds and light journal pressures,
but are not suitable where appreciable
temperature differences are likely to
be encountered. RC 4 Close running fits are
intended chiefly for running fits on accurate
machinery with moderate surface speeds and
journal pressures, where accurate location
and minimum play are desired. RC 5 RC 6
Basic hole system. Limits are in thousandths of
an inch.
Medium running fits are intended for higher
running speeds, or heavy journal pressures, or
both.
Class RC 5
Class RC 1
Class RC 2
Class RC 4
Class RC 6
Class RC 3
Nominal Size Range in Inches
Standard Limits
Standard Limits
Standard Limits
Standard Limits
Standard Limits
Standard Limits
Limits of Clearance
Limits of Clearance
Limits of Clearance
Limits of Clearance
Limits of Clearance
Limits of Clearance
Shaft g4
Shaft g5
Shaft f7
Hole H8
Shaft e7
Hole H5
Hole H6
Shaft f6
Hole H8
Hole H9
Shaft e8
Hole H7
0 - 0.12 0.1 0.2 - 0.1
0.1 0.25 - 0.1 0.3 0.4 - 0.3
0.3 0.6 - 0.3 0.6 0.6
- 0.6 0.6 1.0 - 0.6
0.45 - 0 - 0.25 0.55 - 0
- 0.3 0.95 - 0 - 0.55 1.3
- 0 - 0.7 1.6 - 0 - 1.0
2.2 - 0 - 1.2 0.12 - 0.24
0.15 0.2 - 0.15 0.15 0.3 - 0.15
0.4 0.5 - 0.4 0.4 0.7 -
0.4 0.8 0.7 - 0.8 0.8
1.2 - 0.8 0.5 -
0 - 0.3 0.65 - 0 - 0.35 1.12
- 0 - 0.7 1.6 - 0 - 0.9
2.0 - 0 - 1.3 2.7 - 0
- 1.5 0.24 - 0.40 0.2 0.25 - 0.2
0.2 0.4 - 0.2 0.5 0.6
- 0.5 0.5 0.9 - 0.5 1.0
0.9 - 1.0 1.0 1.4 - 1.0
0.6 - 0 - 0.35 0.85
- 0 - 0.45 1.5 - 0 - 0.9
2.0 - 0 - 1.1 2.5 - 0
- 1.6 3.3 - 0 - 1.9 0.40 -
0.71 0.25 0.3 - 0.25 0.25
0.4 - 0.25 0.6 0.7 - 0.6 0.6
1.0 - 0.6 1.2 1.0 - 1.2
1.2 1.6 - 1.2
0.75 - 0 - 0.45 0.95 - 0 -
0.55 1.7 - 0 - 1.0 2.3 -
0 - 1.3 2.9 - 0 - 1.9
3.8 - 0 - 2.2 0.71 - 1.19 0.3
0.4 - 0.3 0.3 0.5 - 0.3
0.8 0.8 - 0.8 0.8 1.2 -
0.8 1.6 1.2 - 1.6 1.6
2.0 - 1.6 0.95 -
0 - 0.55 1.2 - 0 - 0.7 2.1
- 0 - 1.3 2.8 - 0 -
1.6 3.6 - 0 - 2.4 4.8
- 0 - 2.8 1.19 - 1.97 1.97 - 3.15
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ISO Tolerance Designation

• The ISO system provides for
• 21 types of holes (standard tolerances)
  designated by uppercase letters A, B, C, D,
  E....etc. and
• 21 types of shafts designated by the lower case
  letters a, b, c, d, e...etc.

• These letters define the position of the
  tolerance zone relative to the nominal size. To
  each of these types of hole or shaft are applied
  16 grades of tolerance, designated by numbers IT1
  to IT16 - the "Fundamental Tolerances"
• ITn (0.45 x 3 D 0.001 D) Pn
• where D is the mean of the range of diameters and
  Pn is the progression1, 1.6, 2.5, 4.0, 6.0, 10,
  16, 25......etc. which makes each tolerance grade
  approximately 60 of its predecessor.

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For Example

• Experience has shown that the dimensional
  accuracy of manufactured parts is approximately
  proportional to the cube root of the size of the
  part.
• Example
• A hole is specified as ?30 H7
• The H class of holes has limits of .
  i.e. all tolerances start at the nominal size and
  go positive by the amount designated by the IT
  number.
• IT7 for diameters ranging 30- 50 mm

x 0
Tolerance for IT7 (0.45 x 3 40 0.001x 40) 16
0.025 mm
Written on a drawing as ?30 H7
34
Graphical illustration of ISO standard fits
Hole Series H hole Standard
35
Selection of Fits and theISO Hole Basis system

• From the above it will be realized that there are
  a very large number of combinations of hole
  deviation and tolerance with shaft deviation and
  tolerance. However, a given manufacturing
  organization will require a number of different
  types of fit ranging from tight drive fits to
  light running fits for bearings etc. Such a
  series of fits may be obtained using one of two
  standard systems
• The Shaft Basis System
• For a given nominal size a series of fits is
  arranged for a given nominal size using a
  standard shaft and varying the limits on the
  hole.
• The Hole Basis System
• For a given nominal size, the limits on the hole
  are kept constant, and a series of fits are
  obtained by only varying the limits on the shaft.
  
• The HOLE SYSTEM is commonly used because holes
  are more difficult to produce to a given size and
  are more difficult to inspect. The H series
  (lower limit at nominal, 0.00) is typically used
  and standard tooling (e.g. H7 reamers) and gauges
  are common for this standard.

36
ISO Standard "Hole Basis" Clearance Fits
Type of Fit
Hole
Shaft
Loose Running Fits
. Suitable for loose pulleys
H11
c11
and the looser fastener fits where freedom of
assembly is of prime importance
Free Running Fit.
Where accuracy is not
H9
d10
essential, but good for large temperature
variation, high running speeds, heavy journal
pressures
Close Running Fit.
Suitable for lubricated
H8
f7
bearing, greater accuracy, accurate location,
where no substantial temperature difference is
encountered.

Sliding Fits
. Suitable for precision location fits.
H7
g6
Shafts are expensive to manufacture since the
clearances are small and they are not
recommended for running fits except in
precision equipment where the shaft loadings
are very light.

Locational Clearance Fits
. Provides snug fit
H7
h6
for locating stationary parts but can be freely
assembled and disassembled.
37

ISO Standard "Hole Basis Transition Fits
Type of Fit
Hole
Shaft
Locational Transition Fits
. for accurate
H7
k6
location, a compromise between clearance and
interference
Push Fits
. Transition fits averaging little or no
H7
n6
clearance and are recommended for location fits
where a slight interferance can be tolerated for
the purpose, for example, of eliminating
vibration.
ISO Standard "Hole Basis" Interference Fits
Type of Fit
Hole
Shaft
Press Fit
. Suitable as the standard press fit into
H7
p6
ferrous, i.e. steel, cast iron etc., assemblies.

Drive Fit
Suitable as press fits in
H7
s6

material of low modulus of elasticity such as
light alloys.

38

ISO Clearance Fits
39

ISO Transition Fits
40

ISO Interference Fits
41
Flanged Sintered Bronze Plain Bearing
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(No Transcript)
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http//www.McMasterCarr.com
44
On-line Interactive Catalogs
http//www.skf.com/portal/skf/home/products?mainca
talogue1langennewlink1
45
Tolerance Calculation - 'Worst Case Method'
for correct fit in all cases, if manufactured to
specification

46
Worst Case Tolerancing
Shaft in Hole Example
B
A
1. Allowance Smallest Hole Size (A) Largest
Shaft Size (B)
2. Clearance Largest Hole Size (A) Smallest
Shaft Size (B)
A
Lid on Box Example
B
47
Tolerance Calculation - Tensioner Assy. Example
Axial Clearance by Design must be gt 0.01 but lt
0.25
lt0.25
Worst Case Tolerancing
1. Allowance Smallest Hole Size (76.16)
Largest Shaft Size (76.15) 0.01
2. Clearance Largest Hole Size (76.25)
Smallest Shaft Size (76.00) 0.25
48
Surface Properties - Texture and Hardness
Surface Finish
0.4
With Roughness Value (Typically Ra µm or µ)
Basic Surface Texture Symbol
2
With Machining Allowance
Material Removal by Machining
Hardness
Harden HDN - may see symbol Heat Treat
H/T Rockwell HRC, HRA etc or Ra or Rc Brinell
BNL
HDN to 65 HRC 0.125 DP
0.4
49
Comparative Roughness Values
Roughness Ra Typical Processes 25 µm (1000
µ) Flame Cutting 12.5 µm (500µ) Sawing, sand
casting, 6.3 µm (250µ) forging, shaping,
planing 3.2 µm (125µ) Rough machining, milling,
rough turning, drilling, and die casting 1.6 µm
(63µ) Machining, turning, milling, die and
investment casting, injection molding, and
stamping 0.8 µm (32µ) Grinding, fine turning
milling, reaming, honing, injection molding,
stamping, investment casting 0.4 µm
(16µ) Diamond Turning, Grinding, lapping,
honing 0.2 µm (8µ) Lapping, honing,
polishing 0.1 µm (4µ) Superfinishing, polishing,
lapping
50
Some Common Steel, Hardness and Surface Finish
Specs.
Common Types
Common Steel Specs (10xx series xx
carbon) Mild steel (low carbon up to 30 ) Low
cost general purpose applications, typ.
hardening not required Medium Carbon (up to 60)
requiring higher strength e.g. gears, axles,
con-rods etc. High Carbon (gt 60) High wear,
high strength e.g. cutting tools, springs
etc. Ground Bearing Shaft Examples General
Purpose 1060 Surface HDN to 55 HRC 0.125 mm
deep min. 0.4 µm (16 µ) 303 Stainless
(natural surface hardness 5 HRC ) 0.4µm (16
µ) Better Finish, Longer Life 1020 Case HDN to
65 HRC 0.25 mm deep min. 0.2µm (8 µ) 440
Stainless (natural circa 15 HRC) 0.2µm (8 µ)
1020
1040, 1060
1080
51
Specifying Welds on Drawings
Width of weld